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Originally published in Interiors & Sources

03/20/2013

6 Sources of Central Cooling Savings

Cut costs and increase efficiency with ENERGY STAR’s upgrade tips

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Buying green-certified cooling equipment can be a smart move, but it’s not the whole story. For the best performance, root out additional savings from pumps, fans, and operational practices.

Try these tips from ENERGY STAR to get you started.

1) Consider Capacity

Review the capacity of all chillers, then turn them on or off as needed to keep each one in its most efficient zone. If you have a chilled water plant with excess capacity, consider running condenser water over as many towers as possible, as often as possible, at the lowest speed you can. However, this can cause extra fan cycling, which adds wear to motors and gears.

2) Watch Outdoor Factors
Monitor the conditions outdoors and reset chilled and condenser water temperatures accordingly. The condenser strategy in particular requires adjustment because higher temperatures decrease the power needed for the cooling tower fan, making that look like a source of savings. However, the chiller’s power needs increase. ENERGY STAR’s Building Upgrade Manual notes that “the optimum operating temperature occurs at the point where these two opposing trends combine to produce the lowest total power use.”

3) Keep Up with Cleaning
Scale, algae, and slime can be problematic in many parts of the cooling system and can decrease its efficiency and capacity. Automatic cleaning equipment is available for condensers, while cooling towers may benefit from chemical treatments, ozone generators, and/or ultraviolet irradiation, ENERGY STAR notes.

4) Reduce Resistance
Replace standard valves with low-friction units that can reduce flow resistance for chilled water. This step will reduce pump energy use and return less heat to the chiller.

5) Match Speed to Need
Variable-speed drives help maintain efficiency in pumps and systems where valves control flow by inducing a drop in pressure. If you don’t have sophisticated controls to pair with them, lower chilled-water rates enabled by variable-speed pumps can be coordinated with resetting the chilled water temperature, allowing you to meet loads efficiently.

You can also use the drives in centrifugal compressors, where they’ll let the chiller run at lower speeds under part-load conditions and use less power than a centrifugal chiller with inlet vanes.

6) Higher Efficiency, Lower Energy
Standard or oversized pumps can be replaced with more efficient units after you’ve reduced loads. Most induction motors that drive pumps reach peak efficiency at about 75%.

Hungry for more savings? Check out ENERGY STAR’s free Building Upgrade Manual at www.energystar.gov.

 

 
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